Thermosetting coating composition

ABSTRACT

A thermosetting coating composition comprising an acrylic copolymer (A) containing vinyl monomer units each having an α,β-dicarboxylic acid anhydride group and vinyl monomer units each having an α,β-dicarboxylic monoester group in a total amount of 5-40 wt % and containing the vinyl monomer units with α,β-dicarboxylic acid anhydride groups at 0.3-5 wt %, and an acrylic copolymer (B) with epoxy groups.

TECHNICAL FIELD

The present invention relates to a thermosetting coating compositionwhich is effective as a top clear coating for automobiles and the likefor which attractiveness and a good coating performance are demanded.

BACKGROUND ART

Acryl/melamine-based resins have been widely used as automotive topclear coatings because of their excellent performance in terms ofweather resistance and attractiveness. However, acryl/melamine-basedresins have poor acid resistance because they employ melamine resins ascuring agents and, when applied as paints the coatings become stained byacidic rain, thus impairing the appearance.

In order to overcome this problem, new curing systems have been desiredto replace melamine and therefore much research is being carried out oncuring systems which utilize crosslinking reactions between acid groupsand epoxy groups. For example, in Japanese Unexamined Patent PublicationNo. 63-84674 there is proposed a high solid-content curing compositionwhich contains a low molecular weight polyepoxide, a low molecularweight hydroxyl group-containing polyfunctional substance, acrosslinking agent comprising an acid anhydride, and a curing catalyst,as a paint composition with excellent adhesion, luster and sharpness.Also, Japanese Unexamined Patent Publication No. 1-139653 proposes athermosetting solvent-type coating composition which comprises anacrylic copolymer with acid groups and an acrylic copolymer with epoxygroups, as a coating composition with excellent acid resistance, solventresistance, moisture resistance and coating appearance.

Nevertheless, the use of crosslinking agents containing acid anhydridesas disclosed in Japanese Unexamined Patent Publication No. 63-84674 isassociated with problems in that the increased reactivity between thecomposition components results in poor storage stability, thus making itdifficult to use the composition components in a single solution andreducing handleability. Also, thermosetting solvent-type coatingcompositions such as disclosed in Japanese Unexamined Patent PublicationNo. 1-139653 have poor low-temperature curing properties, and thus whenbaked at the relatively low temperatures employed in automobile bakinglines, they have the disadvantage of exhibiting inadequate coatingperformance, including poor crack resistance, poor acid resistance andpoor solvent resistance, in temperature variable environments.

For the purpose of solving these problems, Japanese Unexamined PatentPublication Nos. 2-45577, 3-287650 and 4-363374 have proposedthermosetting compositions containing copolymers with acid anhydridegroups in the form of half-esters as the acid groups, with hydroxycompounds and epoxy compounds, as well as thermosetting compositionscontaining copolymers with acid anhydride groups in the form ofhalf-esters as acid groups, and compounds with epoxy groups and hydroxygroups. However, since these thermosetting compositions have highcontents of monomer units with half-esterified acid anhydride groups,they are still unsatisfactory from the standpoint of storage stability,while their lack of monomer units with acid anhydride groups presentsthe same disadvantage of insufficient low-temperature curing propertiesand poor solvent resistance.

DISCLOSURE OF THE INVENTION

It is an object of the present invention to provide a thermosettingcoating composition with excellent storage stability and low-temperaturecuring properties, as well as superior coating performance asrepresented by its solvent resistance, acid resistance, scratchresistance, weatherability and attractiveness.

The present inventors have completed the invention as a result ofdiligent research on thermosetting coating compositions in considerationof the aforementioned problems associated with the prior art.

Specifically, the thermosetting coating composition of the presentinvention comprises an acrylic copolymer (A) containing vinyl monomerunits each having an α,β-dicarboxylic acid anhydride group and vinylmonomer units each having an α,β-dicarboxylic monoester group in a totalamount of 5-40 wt % and containing the vinyl monomer units withα,β-dicarboxylic acid anhydride groups at 0.3-5 wt %, and an acryliccopolymer (B) with epoxy groups.

In addition, the inclusion of specific monomer units in the acryliccopolymer (A) and acrylic copolymer (B) mentioned below in thecomposition of the invention provides further improvement in the coatingperformance including acid resistance, solvent resistance andweatherability.

Also, when the thermosetting coating composition of the invention isused as a clear coating in combination with specific base coatings to bedescribed later, a vast improvement in attractiveness is achievedcompared to the use of acrylic/melamine-based coatings of the prior art.

The composition of the invention also has the feature of vastlyimproving the non-sand recoating property as a coating, by addition of ahydroxy group-containing polymer (E) to be specified later.

BEST MODE FOR CARRYING OUT THE INVENTION

The acrylic copolymer (A) used for the thermosetting coating compositionof the invention is obtained either by polymerization of a polymerizablemonomer mixture comprising a dicarboxylic monoester group-containingvinyl monomer and an α,β-dicarboxylic acid anhydride group-containingvinyl monomer, or by polymerization of a polymerizable monomer mixturecontaining an α,β-dicarboxylic acid anhydride group-containing monomer,followed by partial ring opening of the acid anhydride groups with analcohol and monoesterification, and contains the α,β-dicarboxylic acidanhydride group-containing vinyl monomer units and dicarboxylicmonoester group-containing vinyl monomer units, as a total, in the rangeof 5-40 wt %.

If the total of these monomer units is less than 5 wt %, the curingproperty will be insufficient, tending to lower the coating hardness andsolvent resistance, while if it is greater than 40 wt % the storagestability of the thermosetting coating composition will be reduced. Thetotal of the monomer units is preferably in the range of 10-30 wt %.

Also, it is necessary for the vinyl monomer unit with anα,β-dicarboxylic acid anhydride group to be present in a range of 0.3-5wt %. At less than 0.3 wt % of the vinyl monomer unit with an acidanhydride group, the low-temperature curing property will be inadequate,and at greater than 5 wt % the storage stability of the thermosettingcoating composition will be reduced. The content of this monomer unit ispreferably 0.5--3 wt %.

The acrylic copolymer (A) to be used according to the inventionpreferably has an acid value (number of mg of potassium hydroxiderequired to neutralize 1 g of the acrylic copolymer) of 50-150 mgKOH/g,and a weight average molecular weight of 2,000-30,000. If the acid valueof the acrylic copolymer (A) is less than 50 mgKOH/g, the curingproperty may be insufficient, tending to lower the coating hardness andsolvent resistance, while if it is greater than 150 mgKOH/g theviscosity of the copolymer may be notably increased, and the luster,moisture resistance and weatherability resistance of the coating willtend to fall. This value is more preferably in the range of 70-130mgKOH/g. Also, if the weight average molecular weight of the acryliccopolymer (A) is less than 2,000, the moisture resistance andweatherability of the coating may tend to be lower, while if it exceeds30,000 the viscosity of the resin may be notably increased, tending toreduce the attractiveness of the coating and the storage stability ofthe coating composition. This value is more preferably in the range of3,000-20,000.

As specific examples of vinyl monomers with α,β-dicarboxylic acidanhydride groups to be used for acrylic copolymer (A) there may bementioned maleic anhydride, itaconic anhydride, citraconic anhydride and2,3-dimethylmaleic anhydride, and as vinyl monomers with dicarboxylicmonoester groups there may be mentioned monomethyl maleate, monoethylmaleate, monobutyl maleate, monooctyl maleate, monooctyl itaconate,monobutyl fumarate, mono-2-ethylhexyl fumarate and monoethylcitraconate.

As additional vinyl monomers to be used for acrylic copolymer (A) theremay be mentioned, for example, (meth)acrylic esters with hydrocarbonsubstituents such as methyl (meth)acrylate (This expression used hereand throughout includes both methyl acrylate and methyl methacrylate.),ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate,i-butyl (meth)acrylate, t-butyl (meth)acrylate, sec-butyl(meth)acrylate, n-pentyl (meth)acrylate, lauryl (meth)acrylate, tridecyl(meth)acrylate, decyl (meth)acrylate, stearyl (meth)acrylate,2-ethylhexyl (meth)acrylate, cyclohexyl (meth)acrylate, norbornyl(meth)acrylate, isobornyl (meth)acrylate and dicyclopentanyl(meth)acrylate; styrene derivatives such as styrene, vinyltoluene andα-methylstyrene; ethylenic unsaturated nitrile compounds such asacrylonitrile and methacrylonitrile; N-alkoxy-substituted amides such asN-methoxymethyl acrylamide, N-ethoxymethyl acrylamide and N-butoxymethylacrylamide; vinyl basic monomers such as dimethylaminoethyl(meth)acrylate and diethylaminoethyl (meth)acrylate; epoxygroup-containing monomers such as glycidyl (meth)acrylate,methylglycidyl (meth)acrylate, 3,4-epoxycyclohexyl (meth)acrylate andallylglycidyl ether; carboxyl group-containing α,β-unsaturated vinylicmonomers such as methacrylic acid, acrylic acid, crotonic acid,vinylbenzoic acid, fumaric acid, itaconic acid and maleic acid; andlong-chain carboxyl group-containing vinyl monomers, includinghalf-esterified reaction products of acid anhydride compounds andcaprolactone-modified hydroxyl group-containing (meth)acrylic acidesters such as succinic acid monoesters obtained by esterification ofthe terminal hydroxyl group of a ε-caprolactone or γ-buytrolactonering-opening addition product to 2-hydroxyethyl (meth)acrylate,β-carboxyethyl (meth)acrylate, β-(meth)acryloxyethyl acid succinate,β-(meth)acryloxyethyl acid maleate, β-(meth)acryloxyethyl acidphthalate, β-(meth)acryloxyethyl hexahydrophthalate,γ-(meth)acryloxypropyl acid succinate or 2-hydroxyethyl (meth)acrylatewith succinic anhydride to introduce a terminal carboxyl group, andphthalic acid monoesters and hexahydrophthalic anhydride monoestersobtained by esterification of the terminal hydroxyl group of aε-caprolactone or γ-buytrolactone ring-opening addition product (forexample, Placcel F monomer by Daicel Chemicals, KK. or Tone M monomer byUCC Co.) to 2-hydroxyethyl (meth)acrylate with phthalic anhydride orhexahydrophthalic anhydride. These may be used either alone or incombinations of two or more as necessary, but the variouscharacteristics including coating hardness, acid resistance, weatherresistance and solvent resistance can be further improved by using(meth)acrylic acid ester monomers with alicyclic hydrocarbonsubstituents such as cyclohexyl (meth)acrylate, norbornyl(meth)acrylate, isobornyl (meth)acrylate and dicyclopentanyl(meth)acrylate, and adding them as monomer units in the acryliccopolymer (A) to an amount of 10-70 wt %. In this case, it isundesirable for the (meth)acrylic acid ester monomer unit with thealicyclic hydrocarbon substituent to be present at less than 10 wt % asthis may result in an unsatisfactory effect of improvement in thevarious characteristics, or greater than 70 wt % as this may cause thecoating to become brittle, tending to lower the weather resistance andnon-sand recoating property of the coating. The amount is morepreferably in the range of 20-60 wt %.

According to the invention, by inclusion of the aforementionedα,β-dicarboxylic acid anhydride group or dicarboxylic acid monoestergroup with the long-chain carboxylic group and epoxy group in theacrylic copolymer (A), it is possible to increase the reactivity of thecoating composition without impairing its storage stability, thusimproving its low-temperature curing property as well as the scratchresistance, solvent resistance and the hardness of the resultingcoating. In this case, the acid value of the acrylic copolymer (A) ispreferably 50-150 mgKOH/g as mentioned earlier, and the epoxy equivalentvalue (number of grams of resin containing 1 gram equivalent of epoxygroups) is preferably 2,000 g/eq or greater. If the epoxy equivalentvalue of the acrylic copolymer (A) is less than 2,000 g/eq, thethermosetting covering composition may become thickened and prone togelation, while gelation may also tend to occur during synthesis of theacrylic copolymer (A).

The acrylic copolymer (B) to be used in the thermosetting coatingcomposition of the invention is obtained by copolymerization of a vinylmonomer with epoxy groups.

As epoxy-containing vinyl monomers to be used for acrylic copolymer (B)there may be mentioned, for example, glycidyl (meth)acrylate,methylglycidyl (meth)acrylate, 3,4-epoxycyclohexyl (meth)acrylate andallylglycidyl ether, which may be used alone or in combinations of 2 ormore as necessary. The amount of the epoxy-containing monomer used ispreferably in a range of 200-1,500 g/eq in terms of epoxy equivalents ofthe acrylic copolymer (B), and for example it may be in the range of15-60 wt %, or more preferably in the range of 20-50 wt %.

As additional vinyl monomers to be used for acrylic copolymer (B) theremay be mentioned, for example, (meth)acrylic esters with hydrocarbonsubstituents such as methyl (meth)acrylate, ethyl (meth)acrylate,n-propyl (meth)acrylate, n-butyl (meth)acrylate, i-butyl (meth)acrylate,t-butyl (meth)acrylate, sec-butyl (meth)acrylate, n-pentyl(meth)acrylate, lauryl (meth)acrylate, tridecyl (meth)acrylate, decyl(meth)acrylate, stearyl (meth)acrylate, 2-ethylhexyl (meth)acrylate,cyclohexyl (meth)acrylate, norbornyl (meth)acrylate, isobornyl(meth)acrylate and dicyclopentanyl (meth)acrylate; styrene derivativessuch as styrene, vinyltoluene and a-methylstyrene; ethylenic unsaturatednitrile compounds such as acrylonitrile and methacrylonitrile;N-alkoxy-substituted amides such as N-methoxymethyl acrylamide,N-ethoxymethyl acrylamide and N-butoxymethyl acrylamide; basic vinylmonomers such as dimethylaminoethyl (meth)acrylate and diethylaminoethyl(meth)acrylate; hydroxyalkyl group-containing (meth)acrylic acid esterssuch as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate,3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate,4-hydroxybutyl (meth)acrylate and 6-hydroxyhexyl (meth)acrylate;γ-butyrolactone ring-opening addition products to 2-hydroxyethylmethacrylate; ε-caprolactone ring-opening addition products to2-hydroxyethyl acrylate; ethylene oxide ring-opening addition productsto methacrylic acid; propylene oxide ring-opening addition products tomethacrylic acid; (meth)acrylic acid esters with terminal hydroxylgroups, such as 2-hydroxyethyl (meth)acrylate or 2-hydroxypropyl(meth)acrylate dimers or trimers; other hydroxy group-containing vinylmonomers such as 4-hydroxybutyl vinyl ether or p-hydroxystyrene;monobasic or dibasic acid vinyl monomers of methacrylic acid, acrylicacid, crotonic acid, vinylbenzoic acid, fumaric acid, itaconic acid,maleic acid or citraconic acid; monoesters of dibasic acid and acidanhydride group-containing vinyl monomers, such as monomethyl maleate,monoethyl maleate, monobutyl maleate, monooctyl maleate, monomethylitaconate, monoethyl itaconate, monobutyl itaconate, monooctylitaconate, mono-2-ethylhexyl itaconate, monomethyl fumarate, monoethylfumarate, monobutyl fumarate, monooctyl fumarate or monoethylcitraconate; and long-chain carboxyl group-containing vinyl monomers,including half-esterified reaction products of acid anhydrides andcaprolactone-modified hydroxyl group-containing (meth)acrylic acidesters such as succinic acid monoesters obtained by esterification ofthe terminal hydroxyl group of a ε-caprolactone or γ-buytrolactonering-opening addition product to β-carboxyethyl (meth)acrylate,β-carboxypropyl (meth)acrylate, β-(meth)acryloxyethyl acid succinate,β-(meth)acryloxyethyl acid maleate, β-(meth)acryloxyethyl acidphthalate, β-(meth)acryloxyethyl acid hexahydrophthalate,β-(meth)acryloxyethyl acid methylhexahydrophthalate,γ-(meth)acryloxypropyl acid succinate or 2-hydroxyethyl (meth)acrylatewith succinic anhydride to introduce a terminal carboxyl group, andphthalic acid monoesters and hexahydrophthalic anhydride monoestersobtained by esterification of the terminal hydroxyl group of aε-caprolactone or γ-buytrolactone ring-opening addition product (forexample, Praxel F monomer by Dicell Chemicals, KK. or Tone M monomer byUCC Co.) to 2-hydroxyethyl (meth)acrylate with phthalic anhydride orhexahydrophthalic anhydride. These may be used either alone or incombinations of 2 or more as necessary, but the various characteristicsincluding coating hardness, acid resistance, weather resistance andsolvent resistance can be further improved by using (meth)acrylic acidester monomers with alicyclic hydrocarbon substituents such ascyclohexyl (meth)acrylate, norbornyl (meth)acrylate, isobornyl(meth)acrylate and dicyclopentanyl (meth)acrylate, and adding them asmonomer units in the acrylic copolymer (B) to an amount of 10-60 wt %.In this case, it is undesirable for the (meth)acrylic acid ester monomerunit with the alicyclic hydrocarbon substituent to be present at lessthan 10 wt % as this may result in an unsatisfactory effect ofimprovement in the various characteristics, or greater than 70 wt % asthis may cause the coating to become brittle, tending to lower theweatherability and non-sand recoating property of the coating. Theamount is more preferably in the range of 20-50 wt %.

By using hydroxyl group-containing vinyl monomers or carboxylgroup-containing vinyl monomers as other polymerizable monomers in thecomposition of the invention to include hydroxyl groups or carboxylgroups in addition to epoxy groups in the acrylic copolymer (B), it ispossible to increase the reactivity of the coating composition withoutimpairing its storage stability, thus improving its low-temperaturecuring property as well as the solvent resistance and hardness of theresulting coating. The effect can be even further enhanced by using thehydroxyl group-containing vinyl monomers and carboxyl group-containingvinyl monomers to include epoxy groups, hydroxyl groups and carboxylgroups in the acrylic copolymer (B).

According to the invention, the epoxy equivalent value of the acryliccopolymer (B) is preferably 200-1,500 g/eq or greater, and the weightaverage molecular weight is preferably 1,000-20,000. This is because, ifthe epoxy equivalent value of the acrylic copolymer (B) exceeds 1,500g/eq, the curing property may be inadequate, tending to lower thecoating hardness and solvent resistance, while, if it is less than 200g/eq, the covering composition may become thickened and prone togelation; a more preferred range is 250-950 g/eq.

Also, if the weight average molecular weight of the acrylic copolymer(B) is less than 1,000, the moisture resistance and weatherability ofthe coating may tend to fall, and if it exceeds 20,000 the viscosity ofthe resin may be notably increased, tending to reduce the attractivenessand solvent resistance of the covering composition; a more preferablerange is 3,000-15,000.

When hydroxyl groups or carboxyl groups are included in the acryliccopolymer (B), the hydroxyl group equivalent value is preferably in therange of 400-6,000 g/eq. If the hydroxyl group equivalent value of theacrylic copolymer (B) is less than 400 g/eq the moisture resistance maybe lower, while if it is greater than 6,000 g/eq the non-sand recoatingproperty may tend to be reduced; a more preferable range is 500-3000g/eq.

The acid value of the acrylic copolymer (B) is preferably no greaterthan 50 mgKOH/g. If the acid value exceeds 50 mgKOH/g the coveringcomposition may be thickened, and thus prone to gelation.

The weight ratio of the acrylic copolymer (A) and acrylic copolymer (B)in the thermosetting coating composition of the invention is preferablyin the range of 1/3≦(A)/(B)≦10/3. If the weight ratio of the acryliccopolymer (A) and acrylic copolymer (B) is less than 1/3 the storagestability and coating moisture resistance may tend to be lower, while ifit exceeds 10/3 the coating solvent resistance and hardness may tend tobe lower; a more preferred range is 1/2≦(A)/(B)≦4/2.

The molar ratio of carboxyl groups and epoxy groups present in theacrylic copolymer (A) and acrylic copolymer (B) of the thermosettingcovering composition of the invention is preferably in the range of1/2≦carboxyl groups/epoxy groups≦1/0.5. It is preferably not outside ofthis range, as the unreacted functional groups may tend to lower thecoating moisture resistance and weather resistance. A more preferablerange is 1/1.8≦carboxyl groups/epoxy groups≦1/0.7.

Also, the coating moisture resistance and temperature variation crackingresistance can be still further increased by using a methacrylic acidester monomer represented by general formula [I] below as the vinylmonomer constituent of the acrylic copolymer (A) in the thermosettingcoating composition of the invention, added in an amount of 5-50 wt % interms of monomer units, and by using a methacrylic acid ester monomerrepresented by the following general formula [I] as the vinyl monomerconstituent of the acrylic copolymer (B) in the thermosetting coatingcomposition of the invention, added in an amount of 0-25 wt % in termsof monomer units. ##STR1## wherein R¹ represents a hydrocarbon group of8-18 carbon atoms.

Here, it is not preferable for the amount of methacrylic acid estermonomer units of general formula [I] in the acrylic copolymer (A) to beless than 5 wt %, as the above-mentioned effect of improved performancemay be insufficient, or for it to be greater than 50 wt %, as thecoating hardness and solvent resistance may tend to fall. It is also notpreferable for the amount of methacrylic acid ester monomer units ofgeneral formula [I] in the acrylic copolymer (B) to be greater than 25wt %, as the coating hardness and solvent resistance may tend to belower.

In addition, the coating acid resistance, solvent resistance and scratchresistance can be still further increased by using styrene as the vinylmonomer constituent of the acrylic copolymer (A) and acrylic copolymer(B) in the thermosetting coating composition of the invention, each inan amount of 5-25 wt % in terms of monomer units. It is not preferredfor the amount of styrene to be less than 5 wt % as the effect ofimproved performance may be insufficient, or for it to be greater than25 wt % as the coating weatherability may tend to be lower.

For further improvement in the yellowing resistance and non-sandrecoating property, a hydroxyl group-containing polymer (E) may be addedto the thermosetting coating composition of the invention in a range of0.5-30 wt % with respect to the total amount of the acrylic copolymers(A) and (B). If the hydroxyl group-containing polymer (E) is added atless than 0.5 wt % with respect to the total amount of the acryliccopolymers (A) and (B), the improvement effect on the yellowingresistance and non-sand recoating property of the coating may beinadequate, while if it is added at greater than 30 wt % the coatinghardness and solvent resistance may tend to be lower; a more preferablerange is 5-20 wt %.

As useful hydroxyl group-containing polymers (E) there may be mentionedhydroxyl group-containing acrylic copolymers, hydroxyl group-containingpolyester resins and hydroxyl group-containing epoxy resins. In the caseof an acrylic copolymer, examples of hydroxyl group-containing vinylmonomers to be used include hydroxyalkyl group-containing (meth)acrylicacid esters such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl(meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl(meth)acrylate, 4-hydroxybutyl (meth)acrylate and 6-hydroxyhexyl(meth)acrylate; γ-butyrolactone ring-opening addition products to2-hydroxyethyl methacrylate; ε-caprolactone ring-opening additionproducts to 2-hydroxyethyl acrylate; ethylene oxide ring-openingaddition products to methacrylic acid; propylene oxide ring-openingaddition products to methacrylic acid; (meth)acrylic acid esters withterminal hydroxyl groups, such as 2-hydroxyethyl (meth)acrylate or2-hydroxypropyl (meth)acrylate dimers or trimers and other hydroxygroup-containing vinyl monomers such as 4-hydroxybutyl vinyl ether orp-hydroxystyrene; these may be used alone or in combinations of 2 ormore as necessary. The amount of these hydroxyl group-containingmonomers to be used is preferably in a range of 250-1,000 g/eq in termsof hydroxy equivalents of the acrylic copolymer, and for example it maybe in the range of 10-50 wt %, or more preferably in the range of 15-40wt %. When a polyester resin or epoxy resin is used, the hydroxyequivalent value is also preferably in the range of 250-1,000 g/eq. Thisis,because if the hydroxy equivalent value of the hydroxylgroup-containing polymer (E) is greater than 1,000 g/eq the coatingnon-sand recoating property and solvent resistance may tend to be lower,whereas if it is less than 250 g/eq the coating moisture resistance maytend to be lower.

As additional polymerizable vinyl monomers to be used for the acryliccopolymer in the hydroxyl group-containing polymer (E) there may bementioned, for example, (meth)acrylic acid esters with hydrocarbonsubstituents such as methyl (meth)acrylate, ethyl (meth)acrylate,n-propyl (meth)acrylate, n-butyl (meth)acrylate, i-butyl (meth)acrylate,t-butyl (meth)acrylate, sec-butyl (meth)acrylate, n-pentyl(meth)acrylate, lauryl (meth)acrylate, tridecyl (meth)acrylate,2-ethylhexyl (meth)acrylate and cyclohexyl (meth)acrylate; styrenederivatives such as styrene, vinyltoluene and α-methylstyrene; ethylenicunsaturated nitrile compounds such as acrylonitrile andmethacrylonitrile; N-alkoxy-substituted amides such as N-methoxymethylacrylamide, N-ethoxymethyl acrylamide and N-butoxymethyl acrylamide;basic vinyl monomers such as dimethylaminoethyl (meth)acrylate anddiethylaminoethyl (meth)acrylate; monobasic or dibasic acid vinylmonomers of methacrylic acid, acrylic acid, crotonic acid, vinylbenzoicacid, fumaric acid, itaconic acid, maleic acid or citraconic acid; vinylmonomers containing dicarboxylic acid monoester groups such asmonomethyl maleate, monoethyl maleate, monobutyl maleate, monooctylmaleate and monomethyl itaconate; the long-chain carboxylgroup-containing vinyl monomers listed for acrylic copolymer (A), andepoxy group-containing monomers such as glycidyl (meth)acrylate,methylglycidyl (meth)acrylate, 3,4-cyclohexyl-methyl(meth)acrylate andallylglycidyl ether. These may be used alone or in combinations of 2 ormore as necessary.

The acrylic copolymers (A), (B) and (E) to be used in the composition ofthe invention may be produced by any known polymerization methodincluding solution polymerization, bulk polymerization and emulsionpolymerization, but solution polymerization is the most preferred methodof production. When the aforementioned acrylic copolymers are producedby solution polymerization, a common organic solvent such asisopropanol, n-butanol, toluene or xylene may be selected for use. Thepolymerization initiator used may be selected from commonly usedpolymerization initiators such as azobisisobutyronitrile, benzoylperoxide and cumene hydroperoxide. If necessary, a chain transfer agentsuch as 2-mercaptoethanol or n-octylmercaptane may also be used.

When the acrylic copolymers are produced by solution polymerization, itis generally preferred to conduct the polymerization in a temperaturerange of 80-160° C., and more preferably in a range of 100-140° C., formolecular weight control. For production of acrylic copolymerscontaining carboxyl groups and epoxy groups, simultaneouscopolymerization of a carboxyl group-containing vinyl monomer and anepoxy group-containing vinyl monomer may notably increase the viscosityby reaction between the carboxyl groups and epoxy groups duringpolymerization and tend to produce gelation, and therefore the contentof carboxyl groups and epoxy groups in the copolymer may be limited to avery low amount. Consequently, when epoxy groups are included in theacrylic copolymer (A) of the invention, a two-stage polymerizationmethod is preferably used wherein the carboxyl group-containing vinylmonomers are copolymerized at a temperature of at least 100° C., andthen the epoxy group-containing vinyl monomers are polymerized at alower polymerization temperature of under 75° C. Similarly, whencarboxyl groups are included in the acrylic copolymer (B) of theinvention, a two-stage polymerization method is preferably used whereinthe epoxy group-containing vinyl monomers (including, if necessary,hydroxyl group-containing monomers) are copolymerized at a temperatureof at least 100° C., and then the carboxyl group-containing vinylmonomers are polymerized at a lower polymerization temperature of under75° C.

Auxiliary curing agents such as melamine resins or block isocyanateresins may also be added if necessary to the thermosetting coatingcomposition of the invention. These may be added in suitable amountswhich do not impair the storage stability or coating performance of thecoating composition. A preferred amount for their addition is no greaterthan 20 wt % with respect to the total amount of the acrylic copolymers(A) and (B). This is because, when auxiliary curing agents are added atgreater than 20 wt %, the coating acid resistance tends to be lower andthe coating may become prone to yellowing. In addition to the auxiliarycuring agents referred to above, there may also be mentioned epoxycompounds such as glycidyl ethers, glycidyl esters and alicyclic epoxycompounds, and terminal carboxyl group-containing polyester resins withacid values of 100-200 mg/KOH. These auxiliary curing agents may also beused in mixtures of 2 or more.

A catalyst for curing acceleration may also be added to thethermosetting coating composition of the invention. The curing catalystmay be any known catalyst used for an esterification reaction of acidgroups and ester groups, and preferred examples are quaternary ammoniumsalts and phosphonium salts. Specifically there may be mentionedbenzyltrimethylammonium chloride, benzyltrimethylammonium bromide,tetrabutylammonium chloride, tetrabutylammonium bromide,tetrabutylammonium hydroxide, benzyltriphenylphosphonium chloride andbenzyltriphenylphosphonium bromide.

For improved stability, an acidic compound such as a sulfonic acid-basedor phosphoric acid-based compound may be added if necessary.Specifically there may be mentioned para-toluenesulfonic acid,dodecylbenzenesulfonic acid, dinonylnaphthalenesulfonic acid and theiramine blocked compounds, and monoalkylphosphoric acids,dialkylphosphoric acids and monoalkylphosphorous acids.

In addition, other additives, including rheology modifiers such asorganic bentone, polyamides, microgels and fibrinogen-based resins,surface modifiers represented by silicone, ultraviolet absorbers, lightstabilizers, antioxidants, anti-drip agents, may also be added ifnecessary to the thermosetting coating composition of the invention, bypublicly known means and in suitable amounts.

When the thermosetting coating composition of the invention is to beused as a clear coating for automobile finishing, the base coat layeradjacent to the clear coat layer may also be a thermosetting coatingcomposition according to the invention, but known curing resins may alsobe used in appropriate amounts as necessary. The base coating can bemodified by addition of such thermosetting resins with diluting agentscomprising volatile organic solvents, curing agents comprising aminoresins or polyisocyanate compounds, brightening agents such as aluminumpaste, mica and flake-like iron oxide, inorganic and organic pigmentssuch as titanium oxide, carbon black and quinacridone, resin additivessuch as polyester resins, epoxy resins and cellulose resins, as well assurface modifiers, ultraviolet absorbers and antioxidants, inappropriate amounts as necessary using known means.

When the thermosetting coating composition used as a base coat hasN-alkoxyalkyl-substituted amide groups as reactive functional groups,vastly improved attractiveness may be achieved with a multilayer coatingwhereby the thermosetting coating composition of the invention is formedby the 2-coat 1-bake coating method.

Specifically, N-methoxymethyl acrylamide, N-methoxymethylmethacrylamide, N-ethoxymethyl acrylamide, N-propoxymethyl acrylamide orN-butoxymethyl acrylamide, for example, may be used as theN-alkoxyalkyl-substituted amide group-containing vinyl monomer forappropriate polymerization with another vinyl monomer which iscopolymerizable with the amide-based monomer, to obtain an acryliccopolymer as the major component of the thermosetting coveringcomposition.

The amount of the amide-based monomer to be used may be in a range of5-50 wt %. If the amide-based monomer is used at less than 5 wt % thecrosslinked density of the coating may be lower, resulting in a lowerlevel of solvent resistance and non-sand recoating property, while if itis used at over 50 wt % the coating moisture resistance may tend to belower. The amount is preferably in the range of 15-40 wt %.

The specific monomers mentioned above to be used for acrylic copolymer(A) may generally be used as the other copolymerizable vinyl monomer aswell.

Also, if the thermosetting coating composition used as a base coatincludes an acrylic copolymer (C) containing at least 2 carboxyl groupsper molecule and an acrylic copolymer (D) containing at least 2 epoxygroups per molecule in a total amount of 10-50 wt % of the 2 componentswith respect to the resin solid portion of the thermosetting coatingcomposition, vastly improved attractiveness may be achieved formultilayer coatings in which a thermosetting coating composition of theinvention is used as a clear coat.

If the total of the acrylic copolymer (C) and acrylic copolymer (D)constituents of the thermosetting coating composition used as the basecoat is less than 10 wt %, the effect of improved attractiveness may beinadequate, while if it exceeds 50 wt % the storage stability of thethermosetting covering composition may be undesirably lowered.

The acrylic copolymer (C) may be obtained by appropriate polymerizationof the aforementioned dicarboxylic acid monoester group-containing vinylmonomers given as specific examples of monomers to be used for acryliccopolymer (A) or other carboxyl group-containing vinyl monomers, withother vinyl monomers which are copolymerizable therewith, and its acidvalue is preferred to be in the range of 30-150 mgKOH/g. The acryliccopolymer (D) may be obtained by appropriate polymerization of theaforementioned epoxy group-containing vinyl monomers mentioned foracrylic copolymer (B) with other vinyl monomers which arecopolymerizable therewith, and it preferably has an epoxy equivalentvalue in the range of 400-1,500 g/eq. The mixing ratio for the acryliccopolymers (C) and (D) is preferably adjusted so that the equivalentratio of carboxyl groups and epoxy groups is 1/2≦carboxyl groups/epoxygroups≦2. If necessary, the aforementioned quaternary ammonium salts orphosphonium salts may be used as curing catalysts, and a melamine resinmay also be used in an amount of no more than 20 wt % with respect tothe total amount of the acrylic copolymers (C) and (D). Also, volatileorganic solvents, pigments and brightening agents commonly used for basecoats may also be appropriately combined therewith as necessary.

The present invention will now be explained in detail by way ofexamples. The terms "parts" and "%" throughout the examples are allbased on weight.

The properties of the copolymers were evaluated as follows.

Viscosity:

Value as measured with a Gardner-Holt viscometer (25° C.)

Nonvolatile content:

Proportion of nonvolatile matter obtained upon sampling 1 g of resinonto an aluminum dish and drying at 150° C. for one hour.

Hydroxy equivalents:

Number of grams of resin containing 1 gram equivalent of hydroxyl groups

Acid value:

Number of milligrams of potassium hydroxide required to neutralize 1 gof the acrylic copolymer

Epoxy equivalents:

Number of grams of resin containing 1 gram equivalent of epoxy groups

Weight average molecular weight:

Measured by gel permeation chromatography

The characteristics of the coatings were evaluated as follows.

Coating viscosity:

Number of seconds until all the coating in a No. 4 Ford cup dripped off(20° C.)

The coating performance was evaluated in the following manner.

Visual appearance:

Judged primarily based on polished feel and smoothness.

Gloss:

Measured using a digital deformation gloss meter (60° G) manufactured bySuga Testing Equipment, KK.

Hardness:

Hardness measured by scratching the coating at a 45° angle using aMitsubishi Pencil "Uni"

Acid resistance:

Visual determination of spots upon dropwise addition of 40° C. aqueoussulfuric acid solution, allowing to stand at 70° C. for 15 minutes, andwashing with water

Moisture resistance:

Visual judgment of appearance after immersion for 168 hours in 50° C.hot water

Solvent resistance:

Visual judgment of appearance after 50-pass rubbing test using gauzeimmersed in methyl ethyl ketone

Weatherability:

Visual judgment of appearance of coating after 1,500 hour exposure testwith Sunshine Weather-O-Meter manufactured by Suga Testing Equipment, KK

Scratch resistance:

Visual determination of damage upon applying gauze to contact locationsof the coated surface and performing a 10-pass abrasion test with a 1 kgload using a color fastness tester manufactured by Daiei ScientificInstruments, KK.

Storage stability:

Indicates the condition of the coating after standing at 30° C. for 72hours.

⊚ normal

∘ slight viscosity increase but no problem with use

Δ thickening, problems with use

× gelation, unusable

Low-temperature curing property:

Visual judgment of appearance of coating after performing the solventresistance test described above, using xylene on a coated panel baked at120° C.

Non-sand recoating property:

A zinc phosphate-treated steel plate (30 cm×90 cm) was painted with anautomotive cationic electrocoating and baked at 180° C. for 30 minutes.After further coating with an aminoalkyd resin-based second coating andbaking at 160° C. for 30 minutes, the coating was sanded and dried toobtain a test piece.

The test piece was first double-coated with a base coating and a clearcoating by a wet-on-wet system, and after baking for 25 minutes with ahot-air drier at 160° C. and cooling, while still unsanded it was againdouble-coated with the same base coating and clear coating by thewet-on-wet system and baked for 25 minutes with a hot-air drier at 120°C., to form a multilayer coating for evaluation.

Scratches 1 cm square were made in the laminated coating at 1 mmspacings to make 100 square boxes, and after pasting cellophane tapethereover and peeling it off at one stroke, the adhesive property wasevaluated based on the number of squares which remained without peeling.

⊚ no peeling (100/100)

∘ area remaining without peeling at least 95/100

Δ area remaining without peeling at least 50/100 and less than 95/100

× area remaining without peeling less than 50/100

Temperature variation cracking resistance:

A zinc phosphate-treated steel plate (30 cm×90 cm) was coated with anautomotive cationic electrocoating and baked at 180° C. for 30 minutes.After further coating with an aminoalkyd resin-based second coating andbaking at 160° C. for 30 minutes, the coating was sanded and dried toobtain a test piece.

The test piece was first double-coated with a base coating and a clearcoating by a wet-on-wet system, and then baked for 25 minutes with ahot-air drier at 120° C., to form a multilayer coating for evaluation.Upon allowing the coated plate to stand for 30 minutes in a hot-airdrier at 40° C., it was placed in a methanol bath filled with dry ice at-40° C. for rapid cooling. After standing for 30 minutes in the methanolbath, the coating was checked for cracks. The same procedure wasrepeated for 5 cycles.

The numbers represent the number of cycles completed before cracks wereproduced in the coated plate (⊚ signifying no cracking during the 5cycles).

Scale for visual judgment

⊚ no change in quality of coating before and after performance test;judged as maintaining very excellent coating performance.

∘-⊚ virtually no change in quality of coating before and afterperformance test; judged as maintaining excellent coating performed.

∘ quality of coating after performance test slightly lower than beforetest, but judged as exhibiting adequate practical performance.

Δ-∘ quality of coating after performance test lower than before test,but judged as exhibiting adequate practical performance.

×-Δ quality of coating after performance test lower than before test;judged as having problems for practical use.

× quality of coating after performance test notably lower than beforetest; judged as being unsuitable for practical use.

(1) Base coating (M-1) production example

After adding 10 parts of n-butanol and 90 parts of toluene as solventsinto a vessel equipped with an agitator, a temperature control deviceand a condenser, and heating to 100° C. while stirring, a vinylmonomer/polymerization initiator mixture comprising 40 parts of methylmethacrylate, 30 parts of ethyl acrylate, 15 parts of n-butyl acrylate,12 parts of 2-hydroxyethyl methacrylate, 3 parts of methacrylic acid and0.6 part of azobisisobutyronitrile was added dropwise into the solventover a period of 4 hours and then polymerized at the same temperaturefor 3 hours to synthesize an acrylic copolymer (B-1). The nonvolatilecontent of the resulting acrylic copolymer (B-1) was 50%, and its weightaverage molecular weight was 40,000. Next, 100 parts of the acryliccopolymer (B-1), 25 parts of UVAN 20SE-60 (butylated melamine resin,solid portion: 60%, product of Mitsui Toatsu Chemicals, Inc.) and 14parts of Alpaste #1700NL (aluminum paste with solid portion: 65%,product of Toyo Aluminum, KK.) were mixed to obtain a base coatingcomposition. The base coating composition was diluted with a mixedsolvent comprising ethyl acetate/toluene/Solvesso #150 (aromatichydrocarbon, product of Esso Co.) at 40/30/30 (wt %), and the viscosityof the base coating composition was adjusted to 13 seconds with a Fordcup #4, to obtain a silver metallic base coating (M-1).

The amide-crosslinked acrylic copolymer (B-2) havingN-alkoxy-substituted amide groups as reactive functional groups, (B-3)and (B-4) as specific examples of the acrylic copolymer (C) and (B-5) asa specific example of the acrylic copolymer (D) were polymerized withthe monomer compositions listed in Table 6, to obtain resin solutionshaving the characteristic values also listed in Table 6. The coatingcompositions listed in Table 7 were also used to prepare base coatings(M-2) to (M-6) by the same method described for (M-1) above.

(2) Synthesis of acrylic copolymer (P-1)

After adding 20 parts of butyl acetate and 50 parts of Solvesso #100(aromatic petroleum derivative, product of Esso Co.) as solvents into areaction vessel equipped with an agitator, a temperature control deviceand a condenser, and heating to 100° C. while stirring, amonomer/polymerization initiator mixture comprising 10 parts of methylmethacrylate, 49.1 parts of t-butyl methacrylate, 15 parts of2-ethylhexyl acrylate, 20 parts of maleic anhydride, 30 parts of butylacetate and 3 parts of azobisisobutyronitrile was continuously addeddropwise into the vessel over a period of 4 hours and then polymerizedfor 3 hours while keeping the temperature in the flask at 100° C., for asufficiently high conversion rate to the resin. The temperature in thevessel was then lowered to 70° C., 5.9 parts of methanol and 0.6 part oftriethylamine were further added, and the internal temperature was keptat 70° C. for 7 hours for partial monoesterification of the acidanhydride groups. The reduction in acid anhydride groups was confirmedby IR, and thus an acrylic copolymer (P-1) with a resin solid portion of50% was obtained. The characteristic values of the resulting copolymer(P-1) are shown in Table 1, and this copolymer (P-1) consisted of 23.9parts monomethyl maleate monomer units and 2 parts maleic anhydridemonomer units against 100 parts as the total monomer units.

(3) Synthesis of acrylic copolymers (P-4), (P-6), (P-8), (P-10), (P-13),(P-14), (P-15), (P-19), (P-20)

The vinyl monomers listed in Table 1 were each polymerized according tothe synthesis method for acrylic copolymer (P-1), to synthesize acryliccopolymers (P-4), (P-6), (P-8), (P-10), (P-13), (P-14), (P-15), (P-19)and (P-20). The characteristic values of the resulting copolymers arelisted in Table 1.

(4) Synthesis of acrylic copolymer (P-2)

After adding 45 parts of butyl acetate and 50 parts of Solvesso #100(aromatic petroleum derivative, product of Esso Co.) as solvents into areaction vessel equipped with an agitator, a temperature control deviceand a condenser, and heating to 100° C. while stirring, amonomer/polymerization initiator mixture comprising 15 parts of methylmethacrylate, 44.8 parts of t-butyl methacrylate, 20 parts of2-ethylhexyl acrylate, 10 parts of monobutyl maleate, 1.2 parts ofmaleic anhydride, 5 parts of butyl acetate, 9 parts of methacrylic acidand 3 parts of azobisisobutyronitrile was continuously added dropwiseinto the vessel over a period of 4 hours.

Polymerization was then conducted for 3 hours while keeping thetemperature in the vessel at 100° C., and the reaction was terminatedwhen a sufficiently high conversion rate to the resin was achieved, toobtain acrylic copolymer (P-2). The characteristic values of theresulting acrylic copolymer are listed in Table 1.

(5) Synthesis of acrylic copolymers (P-5), (P-7), (P-9), (P-11), (P-12),(P-16), (P-17), (P-18)

The vinyl monomers listed in Table 1 were each polymerized according tothe synthesis method for acrylic copolymer (P-2), to synthesize acryliccopolymers (P-5), (P-7), (P-9), (P-11), (P-12), (P-16), (P-17) and(P-18). The characteristic values of the resulting copolymers are listedin Table 1.

(6) Synthesis of acrylic copolymer (P-3)

After adding 45 parts of butyl acetate and 50 parts of Solvesso #100 assolvents into a reaction vessel equipped with an agitator, a temperaturecontrol device and a condenser, and heating to 100° C. while stirring, amonomer/polymerization initiator mixture comprising 4.5 parts of methylmethacrylate, 40.2 parts of t-butyl methacrylate, 29.2 parts of2-ethylhexyl acrylate, 12 parts of monobutyl maleate, 5 parts ofmethacrylic acid, 0.8 part of maleic anhydride, 5 parts of butyl acetateand 3 parts of azobisisobutyronitrile was added dropwise into the vesselover a period of 4 hours.

The temperature in the vessel was then lowered to 75° C., amonomer/polymerization initiator mixture comprising 2 parts of glycidylmethacrylate, 0.5 parts of methyl methacrylate, 5 parts of t-butylmethacrylate, 0.8 part of 2-ethylhexyl acrylate and 1 part ofazobismethylvaleronitrile was added dropwise into the vessel over aperiod of 2 hours. After the dropwise addition was completed,polymerization was conducted for 3 hours while keeping the temperaturein the vessel at 75° C., and the reaction was terminated when asufficiently high conversion rate to the resin was achieved, tosynthesize acrylic copolymer (P-3). The characteristic values of theresulting acrylic copolymer are listed in Table 1.

(7) Synthesis of acrylic copolymer (G-1)

After adding 20 parts of n-butanol and 80 parts of Solvesso #100 assolvents into a reaction vessel equipped with an agitator, a temperaturecontrol device and a condenser, and heating to 120° C. while stirring, amonomer/polymerization initiator mixture comprising 20 parts of methylmethacrylate, 10 parts of n-butyl methacrylate, 20 parts of 2-ethylhexylacrylate, 20 parts of 2-hydroxyethyl methacrylate, 30 parts of glycidylmethacrylate, 3 parts of azobisisobutyronitrile and 7 parts oft-butylperoxy isopropylcarbonate was added dropwise into the vessel overa period of 4 hours, polymerization was conducted for 3 hours whilekeeping the temperature in the vessel at 120° C., and the reaction wasterminated when a sufficiently high conversion rate to the resin wasachieved, to synthesize acrylic copolymer (G-1). The characteristicvalues of the resulting acrylic copolymer are listed in Table 2.

(8) Synthesis of acrylic copolymers (G-2), (G-4)-(G-9), (G-10)-(G-14)

The vinyl monomers listed in Table 2 were each polymerized according tothe synthesis method for acrylic copolymer (G-1), to synthesize acryliccopolymers (G-2), (G-4)-(G-9) and (G-10)-(G-14). The characteristicvalues of the resulting copolymers are listed in Table 2.

(9) Synthesis of acrylic copolymer (G-3)

After adding 20 parts of n-butanol and 80 parts of Solvesso #100 assolvents into a reaction vessel equipped with an agitator, a temperaturecontrol device and a condenser, and heating to 120° C. while stirring, amonomer/polymerization initiator mixture comprising 9 parts of methylmethacrylate, 29.5 parts of n-butyl methacrylate, 9 parts of2-ethylhexyl acrylate, 13.5 parts of 4-hydroxybutyl acrylate, 30 partsof glycidyl methacrylate, 3 parts of azobisisobutyronitrile and 7 partsof t-butylperoxyisopropyl carbonate was added dropwise into the vesselover a period of 4 hours.

The temperature in the vessel was then lowered to 75° C., amonomer/polymerization initiator mixture comprising 1 part of methylmethacrylate, 3.5 parts of n-butyl methacrylate, 1 part of 2-ethylhexylacrylate, 1.5 parts of 4-hydroxybutyl acrylate, 2 parts of methacrylicacid and 1 part of azobismethylvaleronitrile was added dropwise into thevessel over a period of 2 hours. After the dropwise addition wascompleted, polymerization was conducted for 3 hours while keeping thetemperature in the vessel at 75° C., and the reaction was terminatedwhen a sufficiently high conversion rate to the resin was achieved, tosynthesize acrylic copolymer (G-3). The characteristic values of theresulting acrylic copolymer are listed in Table 2.

(10) Synthesis of acrylic copolymers (H-1), (H-3)

The vinyl monomers listed in Table 3 were each polymerized according tothe synthesis method for acrylic copolymer (G-1), to synthesize hydroxylgroup-containing acrylic copolymers. The characteristic values of theresulting copolymers are listed in Table 3.

(11) Synthesis of hydroxyl group-containing polyester resin (H-2)

After charging 44 parts of Cardura E10 (product of Yuka Shell Epoxy,KK.), 41 parts of isophthalic acid, 6 parts of trimethylolpropane and 9parts of 1,6-hexanediol into a reaction vessel equipped with anagitator, a thermometer and a condenser, reaction was conducted in anitrogen gas flow at 220° C. for 10 hours to obtain a polyester resinwith an acid value of 9, a hydroxy equivalent value of 800 and a weightaverage molecular weight of 3500. Xylene was then added for dilution toa nonvolatile content of 60%, giving characteristic values of a Gardnerviscosity of 0, an acid value of 5.4 and a hydroxy equivalent value of1333.

(12) Preparation of clear paints

The acrylic copolymers listed in Tables 1, 2 and 3 (H-2 being apolyester resin) were mixed in the proportions indicated in Tables 4 and9, and after thorough stirring a mixed solvent was added to each(Solvesso #100/cellosolve acetate=80/20 (weight ratio)) for dilution toa coating viscosity of 28 seconds (using a Ford cup No. 4, measuringtemperature: 20° C.) to prepare clear coatings.

                                      TABLE 1                                     __________________________________________________________________________    Acrylic copolymer (A)  P-1 P-2 P-3 P-4 P-5 P-6 P-7 P-8 P-9 P-10               __________________________________________________________________________    Monomer component                                                                       styrene                                          10                           methyl methacrylate                                                                        10  15  5                                                        t-butyl methacrylate                                                                       49.1                                                                              44.8                                                                              45.2                                                     isobornyl methacrylate   40                                                   isobornyl acrylate           48                                               cyclohexyl methacrylate          60      55  50  53.8                         cyclohexyl acrylate                  50                                       2-ethylhexyl acrylate                                                                      15  20  30  40.8                                                                              32  20.6                                                                              24  15.7                                                                              22.3                                                                              10                           2-ethylhexyl                             15.7                                                                              22.3                                                                              10                           methacrylate                                                                  monomethyl maleate*.sup.1                                                                  (23.9)      (17.1)  (17.9)                                                                            25  (27.7)  (25.2)                       monobutyl maleate                                                                              10  12      12                                               monooctyl itaconate                          17.2                             methacrylic acid 9   5       5               8                                glycidyl methacrylate                                                                          2                                                            maleic anhydride                                                                           2   1.2 0.8 2.1 3   1.5 1   1.6 2.5 1                  Solvent   butyl acetate                                                                              50  50  50  50  50  50  50  50  50  50                           Solvesso #100                                                                              50  50  50  50  50  50  50  50  50  50                 Solution  nonvolatile content                                                                        50  50  50  50  50  50  50  50  50  50                           (wt %)                                                                        Gardner viscosity (25° C.)                                                          Y   V   X   V   T   X   U   Y   Y   Y                  copolymer acid value (mgKOH/g)                                                                       103 91  72  74  72  77  108 119 92  108                          epoxy equivalents (g/eq)                                                                           7100                                                     weight average molecular                                                                   10000                                                                             8000                                                                              12000                                                                             16000                                                                             7000                                                                              15000                                                                             10000                                                                             12000                                                                             8000                                                                              11000                        weight                                                              __________________________________________________________________________    Acrylic copolymer (A)  P-11                                                                              P-12                                                                              P-13                                                                              P-14                                                                              P-15                                                                              P-16                                                                              P-17                                                                              P-18                                                                              P-19                                                                              P-20               __________________________________________________________________________    Monomer component                                                                       styrene      15                      20  20  15  15                 (parts by weight)                                                                       methyl methacrylate                                                                            10  10  20  10  20                                           t-butyl methacrylate                                                                           49  46.7                                                                              10  40  40  46  20  35  35                           isobornyl methacrylate                                                        isobornyl acrylate                                                                         32.2                                                             cyclohexyl methacrylate                                                       cyclohexyl acrylate                                                                        32.2                                                             2-ethylhexyl acrylate                                                                          25  20  17.6                                                                              26.1                                                                              26  25  21  24.1                                                                              24.1                         2-ethylhexyl 30                                                               methacrylate                                                                  monomethyl maleate*.sup.1                                                                          (13.3)                                                                            (50.4)                                                                            (15.9)  5       (23.9)                                                                            (23.9)                       monobutyl maleate                                                                          15                  1       25                                   monooctyl itaconate                                                           methacrylic acid                                                                           7   15  10          10  2   12                                   glycidyl methacrylate                                                         maleic anhydride                                                                           0.8 1       2   8   3   2   2   2   2                  Solvent   butyl acetate                                                                              50  50  50  50  50  50  50  50  50  50                           Solvesso #100                                                                              50  50  50  50  50  50  50  50  50  50                 Solution  nonvolatile content                                                                        50  50  50  50  50  50  50  50  50  50                           (wt %)                                                                        Gardner viscosity (25° C.)                                                          X   Z.sub.1                                                                           X   Z   V   Y   Z'  Z.sub.1                                                                           A   Z.sub.6            copolymer acid value (mgKOH/g)                                                                       94  98  122 217 68  68  35  159 103 103                          epoxy equivalents (g/eq)                                                      weight average molecular                                                                   10000                                                                             13000                                                                             7000                                                                              6000                                                                              10000                                                                             11000                                                                             16000                                                                             7000                                                                              1800                                                                              50000                        weight                                                              __________________________________________________________________________     Notes                                                                         *.sup.1 Values in parentheses, as indicated in the production examples,       are monomer units from reaction of methanol with a polymer prepared by        copolymerization of maleic anhydride, and thus consist of a copolymerized     component.                                                                    .sup.2 Acid value and epoxy equivalents converted to resin solid values. 

                                      TABLE 2                                     __________________________________________________________________________    Acrylic copolymer (B)                                                                         G-1                                                                              G-2 G-3                                                                              G-4                                                                              G-5                                                                              G-6                                                                              G-7 G-B G-9                                                                              G-10                                                                             G-11                                                                             G-12                                                                              G-13                                                                             G-14               __________________________________________________________________________    Monomer                                                                             styrene                              15    5         20                 component                                                                           methyl methacrylate                                                                     20 10  10                     10    10                        (parts by                                                                           t-butyl methacrylate                    40    20                        weight)                                                                             n-butyl methacrylate                                                                    10 20  33 10                            20                          norbornyl methacrylate 30                                                     dicyclopentanyl     20                                                        methacrylate                                                                  cyclohexyl                   20  30  25                                       methacrylate                                                                  cyclohexyl acrylate       40                                                  2-ethylhexyl acrylate                                                                   20 10  10 15 20 10 20         20    20                              2-ethylhexyl                         15    15     10 28                       methacrylate                                                                  n-butyl acrylate                                                              lauryl methacrylate              15                                           2-hydroxyethyl         15 20     25        5                                  acrylate                                                                      2-hydroxyethyl                                                                          20        30       20         20    20                              methacrylate                                                                  4-hydroxybutyl                                                                             20  15                  15           40 2                        acrylate                                                                      3,4-epoxycyclohexyl                     10                                    methyl methacrylate                                                           glycidyl methacrylate                                                                   30 40  30 25 35 30 40  30  30    75 30  30 50                       methacrylic acid 2                                                      Solvent                                                                             n-butanol 20 20  20 20 20 20 20  20  20 20 20 20  20 20                       Solvesso #100                                                                           80 80  80 80 80 80 80  80  80 80 80 80  80 80                 Solution                                                                            nonvolatile content                                                                     50 50  50 50 50 50 50  50  50 50 50 50  50 50                       (wt %)                                                                        Gardner visc. (25° C.)                                                           F  P   O  J  H  K  M   P   L  N  G  Z.sub.2                                                                           N  O                  Copolymer                                                                           epoxy eq (g/eq)                                                                         473                                                                              355 473                                                                              568                                                                              406                                                                              473                                                                              355 473 473                                                                              1960                                                                             189                                                                              473 473                                                                              284                      hydroxy eq (q/eq)                                                                       650                                                                              720 960                                                                              433                                                                              773                                                                              580                                                                              650 464 960                                                                              650                                                                              2320                                                                             650 360                                                                              7200                     acid value (mgKOH/g)                                                                           13                                                           wt av. molecular wt                                                                     5000                                                                             12000                                                                             8000                                                                             6000                                                                             7000                                                                             9000                                                                             11000                                                                             13000                                                                             7000                                                                             6000                                                                             3000                                                                             30000                                                                             7000                                                                             12000              __________________________________________________________________________     Note                                                                          *.sup.1 Epoxy equivalents, hydroxy equivalents and acid values converted      to resin solid values.                                                   

                  TABLE 3                                                         ______________________________________                                        Hydroxy group-containing                                                      polymer (E)        H-1      H-2     H-3                                       ______________________________________                                        Monomer  styrene       10             5                                       component                                                                              t-butyl       51             14                                      (parts by                                                                              methacrylate                                                         weight)  2-ethylhexyl  8              20                                               acrylate                                                                      2-hydroxyethyl                                                                              30                                                              acrylate                                                                      2-hydroxyethyl               60                                               methacrylate                                                                  methacrylic acid                                                                            1              1                                                Cardura E10            44                                                     isophthalic acid       41                                                     trimethylolpropane     6                                                      1,6-hexanediol         9                                             Solvent  n-butanol     20       --    20                                               Solvesso #100 80       --    80                                               xylene                 66.7                                          Solution nonvolatile content                                                                         50       60    50                                               (wt %)                                                                        Gardner viscosity                                                                           N        O     R                                                (25° C.)                                                      Copolymer                                                                              hydroxy equivalents                                                                         387      800   217                                              (g/eq)                                                                        acid value    6.5      9     6.5                                              (mgKOH/g)                                                                     wt. average   7000     3500  5000                                             molecular wt.                                                        ______________________________________                                         Note                                                                          *.sup.1 Hydroxy equivalents and acid values converted to resin solid          values                                                                   

Note

*1: Hydroxy equivalents and acid values converted to resin solid values

                                      TABLE 4                                     __________________________________________________________________________                   Example                                                                       1  2  3  4  5  6  7  8  9  10 11 12 13                         __________________________________________________________________________    Acrylic copolymer (A)                                                                        P-1                                                                              P-2                                                                              P-3                                                                              P-1                                                                              P-4                                                                              P-5                                                                              P-1                                                                              P-2                                                                              P-4                                                                              P-5                                                                              P-6                                                                              P-7                                                                              P-8                                       100                                                                              100                                                                              100                                                                              100                                                                              100                                                                              100                                                                              100                                                                              100                                                                              100                                                                              100                                                                              100                                                                              100                                                                              100                        Acrlyic copolymer (B)                                                                        G-1                                                                              G-2                                                                              G-1                                                                              G-3                                                                              G-1                                                                              G-2                                                                              G-4                                                                              G-5                                                                              G-4                                                                              G-5                                                                              G-6                                                                              G-7                                                                              G-8                                        90                                                                               60                                                                               60                                                                               90                                                                               60                                                                               50                                                                              100                                                                               70                                                                               80                                                                               50                                                                               70                                                                               70                                                                              100                        Hydroxy group-containing polymer                                              (E)                                                                           Modaflow*.sup.1                                                                              0.2                                                                              0.2                                                                              0.2                                                                              0.2                                                                              0.2                                                                              0.2                                                                              0.2                                                                              0.2                                                                              0.2                                                                              0.2                                                                              0.2                                                                              0.2                                                                              0.2                        BTBAC*.sup.2   1.0                                                                              0.8                                                                              0.8                                                                              1.0                                                                              0.8                                                                              0.8                                                                              1.0                                                                              0.9                                                                              0.9                                                                              0.8                                                                              0.9                                                                              0.9                                                                              1.0                        Chinubin 900*.sup.3                                                                          2.0                                                                              1.6                                                                              1.6                                                                              2.0                                                                              1.6                                                                              1.6                                                                              2.0                                                                              1.8                                                                              1.8                                                                              1.6                                                                              1.8                                                                              1.8                                                                              2.0                        Sanol 440*.sup.4                                                                             2.0                                                                              1.6                                                                              1.6                                                                              2.0                                                                              1.6                                                                              1.6                                                                              2.0                                                                              1.8                                                                              1.8                                                                              1.6                                                                              1.8                                                                              1.8                                                                              2.0                        Auxiliary                                                                            UVAN 20SE*.sup.5                                                       curing agent                                                                         Denacol EX-212*.sup.6                                                  __________________________________________________________________________                     Example                      Co. Ex.                                          14   15 16   17 18   19 20   15 16                           __________________________________________________________________________    Acrylic copolymer (A)                                                                          P-9  P-10                                                                             P-11 P-1                                                                              P-2  P-1                                                                              P-1  P-1                                                                              P-1                                           100  100                                                                              100  100                                                                              100  100                                                                              100  100                                                                              100                          Acrylic copolymer (B)                                                                          G-8  G-9                                                                              G-9  G-1                                                                              G-2  G-1                                                                              G-1  G-13                                                                             G-14                                           80   90                                                                               80   90                                                                               60   90                                                                               90   90                                                                               60                          Hydroxy group-containing polymer (E)                                                                        H-1        H-2                                                                 30         20                                  Modaflow         0.2  0.2                                                                              0.2  0.2                                                                              0.2  0.2                                                                              0.2  0.2                                                                              0.2                          BTBAC            0.9  1.0                                                                              0.9  1.1                                                                              0.8  1.0                                                                              1.1  1.0                                                                              0.8                          Tinuvin 900      1.8  2.0                                                                              1.8  2.2                                                                              1.6  2.0                                                                              2.2  2.0                                                                              1.6                          Sanol 440        1.8  2.0                                                                              1.8  2.2                                                                              1.6  2.0                                                                              2.2  2.0                                                                              1.6                          Auxiliary                                                                            UVAN 20SE                 5                                            curing agent                                                                         Denacol EX-212                  10      10                             __________________________________________________________________________     Notes:                                                                        *.sup.1 Acrylic surface modifier by Monsanto Co.                              *.sup.2 Benzyltributylammonium chloride                                       *.sup.3 Ultraviolet absorber by CibaGeigy Co.                                 *.sup.4 Light stabilizer by Sankyo, KK.                                       *.sup.5 Butylated melamine resin (solid portion: 60%) by Mitsui Toatsu        Chemicals, KK.                                                                *.sup.6 Aliphatic epoxy resin (solid portion: 100%) by Nagase Chemicals,      KK.                                                                      

                  TABLE 5                                                         ______________________________________                                                 Example                                                                       1     2     3   4   5   6   7   8   9   10   11                      ______________________________________                                        Storage  ∘                                                                       ∘                                                                       ∘                                                                     ∘                                                                     ⊚                                                                  ∘                                                                     ⊚                                                                  ∘                                                                     ⊚                                                                  ∘                                                                      ∘           stability                                                                     Visual   ∘                                                                       ∘                                                                       ∘                                                                     ∘                                                                     ∘                                                                     ∘                                                                     ∘                                                                     ∘                                                                     ∘-.circleincircle                                                 .   ∘-.circleinci                                                     rcle.                                                                              ∘-.circl                                                          eincircle.              appearance                                                                    Luster   95    96    94  94  96  96  95  96  98  98   97                      Hardness F     F     H   H   H   H   H   H   H   H    H                       Acid resistance                                                                        ∘                                                                       ∘                                                                       ∘                                                                     ∘                                                                     ∘-⊚                                                    ∘-⊚                                                    ∘-⊚                                                    ∘-⊚                                                    ∘-.circleincircle                                                 .   ∘-.circleinci                                                     rcle.                                                                              ∘-.circl                                                          eincircle.              Moisture ∘                                                                       ∘                                                                       ∘                                                                     ∘                                                                     ∘-⊚                                                    ∘-⊚                                                    ∘-⊚                                                    ∘-⊚                                                    ∘-.circleincircle                                                 .   ∘-.circleinci                                                     rcle.                                                                              ∘-.circl                                                          eincircle.              resistance                                                                    Solvent  ∘                                                                       ∘                                                                       ∘                                                                     ∘                                                                     ∘-⊚                                                    ∘-⊚                                                    ∘-⊚                                                    ∘-⊚                                                    ∘-.circleincircle                                                 .   ∘-.circleinci                                                     rcle.                                                                              ∘-.circl                                                          eincircle.              resistance                                                                    Weatherability                                                                         ∘                                                                       ∘                                                                       ∘                                                                     ∘                                                                     ∘-⊚                                                    ∘-⊚                                                    ∘-⊚                                                    ∘-⊚                                                    ∘-.circleincircle                                                 .   ∘-.circleinci                                                     rcle.                                                                              ⊚        Non-sand ∘                                                                       ∘                                                                       ∘                                                                     ∘                                                                     ∘                                                                     ∘                                                                     ∘                                                                     ∘                                                                     ∘                                                                     ∘                                                                      ∘           recoating                                                                     property                                                                      Temperature                                                                            ⊚                                                                    ⊚                                                                    ⊚                                                                  ⊚                                                                  ⊚                                                                  ⊚                                                                  ⊚                                                                  ⊚                                                                  ⊚                                                                  ⊚                                                                   ⊚        variation crack                                                               resistance                                                                    Scratch  ∘                                                                       ∘                                                                       ∘                                                                     ∘                                                                     ∘                                                                     ∘                                                                     ∘                                                                     ∘                                                                     ∘-.circleincircle                                                 .   ∘-.circleinci                                                     rcle.                                                                              ∘-.circl                                                          eincircle.              resistance                                                                    Low-tempera-                                                                           ∘                                                                       ∘                                                                       ∘                                                                     ∘                                                                     ∘-⊚                                                    ∘-⊚                                                    ∘-⊚                                                    ∘-⊚                                                    ∘-.circleincircle                                                 .   ∘-.circleinci                                                     rcle.                                                                              ∘-.circl                                                          eincircle.              ture curing                                                                   property                                                                      ______________________________________                                               Example             Co. Ex.                                                     12    13    14  15  16  17  18  19  20  15   16                      ______________________________________                                        Storage  ∘                                                                       ∘                                                                       ∘                                                                     ∘                                                                     ∘                                                                     ⊚                                                                  ∘                                                                     ∘                                                                     ⊚                                                                  ∘                                                                      ∘           stability                                                                     Visual   ∘-⊚                                                      ∘-⊚                                                      ∘-⊚                                                    ∘-⊚                                                    ∘-⊚                                                    ∘                                                                     ∘                                                                     ∘                                                                     ∘                                                                     ∘                                                                      ∘           appearance                                                                    Luster   98    97    98  99  99  94  94  95  95  94   96                      Hardness H     H     H   H   H   F   H   H   F   H    H                       Acid resistance                                                                        ∘-⊚                                                      ∘-⊚                                                      ∘-⊚                                                    ⊚                                                                  ⊚                                                                  ∘                                                                     ∘                                                                     ∘                                                                     ∘                                                                     ∘                                                                      ∘           Moisture ∘-⊚                                                      ⊚                                                                    ⊚                                                                  ⊚                                                                  ⊚                                                                  ∘                                                                     ∘                                                                     ∘                                                                     ∘                                                                     Δ-∘                                                              ∘-.circl                                                          eincircle.              resistance                                                                    Solvent  ∘-⊚                                                      ∘-⊚                                                      ∘-⊚                                                    ⊚                                                                  ⊚                                                                  ∘                                                                     ∘                                                                     ∘                                                                     ∘                                                                     ∘                                                                      ∘           resistance                                                                    Weatherability                                                                         ⊚                                                                    ⊚                                                                    ⊚                                                                  ⊚                                                                  ⊚                                                                  ∘                                                                     ∘                                                                     ∘                                                                     ∘                                                                     ∘                                                                      ∘           Non-sand ∘                                                                       ∘                                                                       ∘                                                                     ∘                                                                     ∘                                                                     ⊚                                                                  ∘                                                                     ∘                                                                     ⊚                                                                  ⊚                                                                   Δ-.smallcircle                                                          .                       recoating                                                                     property                                                                      Temperature                                                                            ⊚                                                                    ⊚                                                                    ⊚                                                                  ⊚                                                                  ⊚                                                                  ⊚                                                                  ⊚                                                                  ⊚                                                                  ⊚                                                                  ⊚                                                                   ⊚        variation crack                                                               resistance                                                                    Scratch  ∘-⊚                                                      ∘-⊚                                                      ∘-⊚                                                    ⊚                                                                  ⊚                                                                  ∘                                                                     ∘                                                                     ∘                                                                     ∘                                                                     ∘                                                                      ∘           resistance                                                                    Low-tempera-                                                                           ∘-⊚                                                      ∘-⊚                                                      ∘-⊚                                                    ⊚                                                                  ⊚                                                                  ∘                                                                     ∘                                                                     ∘                                                                     ∘                                                                     ∘                                                                      ∘           ture curing                                                                   property                                                                      ______________________________________                                         Note: Example 1-22 all employed as the base paint.                       

                  TABLE 6                                                         ______________________________________                                        Acrylic copolymer for base                                                                     B-2     B-3     B-4   B-5                                    ______________________________________                                        Monomer methyl methacrylate                                                                        30      40    50    30                                   composition                                                                           ethyl acrylate             30    45                                   (parts by                                                                             butyl acrylate                                                                             37      46.7                                             weight) 2-hydroxyethyl                                                                             5             10    10                                           acrylate                                                                      monomethyl           (13.3)                                                   maleate*.sup.1                                                                N-butoxymethyl                                                                             25                                                               acrylamide                                                                    glycidyl                         15                                           methacrylate                                                                  methacrylic acid                                                                           3             10                                         Solvent n-butanol    30      --    30    20                                           butyl acetate                                                                              --      50    --    --                                           Solvesso #100                                                                              70      50    70    80                                   Solution                                                                              nonvolatile content                                                                        50      50    50    50                                           (wt %)                                                                        Gardner viscosity                                                                          Z       V     Z     U                                            (25° C.)                                                       Copolymer                                                                             amide equivalents                                                                          628     --    --    --                                           (g/eq)                                                                        acid value   19.5    57    65    --                                           (mgKOH/g)                                                                     epoxy equivalents                                                                          --      --    --    947                                          (g/eq)                                                                        hydroxy equivalents                                                                        2320    --    1160  1160                                         (g/eq)                                                                        wt. average  40000   30000 40000 30000                                        molecular wt.                                                         ______________________________________                                         Note                                                                          *.sup.1 same as note *1 for Table 1                                           *.sup.2 Amide equivalents, acid values, epoxy equivalents and hydroxy         equivalents converted to resin solid values.                             

                  TABLE 7                                                         ______________________________________                                                        M-2  M-3    M-4    M-5  M-6                                   ______________________________________                                        Coating N-alkoxyalkyl-                                                                              B-2    B-2            B-2                               composition                                                                           substituted amide                                                                           100    100            100                               (parts by                                                                             group-containing                                                      weight) acrylic copolymer                                                             acrylic copolymer                                                                           --          B-3  B-4  B-3                                       (C)                        20   20   33                                       acrylic copolymer                                                                           --     --   B-5  B-5  B-5                                       (D)                        20   20   33                                       acrylic copolymer                                                                           --     --   B-1  B-1                                                                      100  100                                            UVAN 20SE*.sup.1                                                                            --     9.3  15   20   --                                        Alpaste #1700NL*.sup.2                                                                      11     12   18   18   18                                        BTBAC*.sup.3  --     --   0.4  0.4  0.8                                       Nacure 4054*.sup.4                                                                          1.0    1.0  1.2  1.2  1.6                               Number of coating dilution                                                                      13     13     13   13   13                                  seconds*.sup.5                                                                ______________________________________                                         Notes:                                                                        *.sup.1 Butylated melamine resin (solid portion: 60%) by Mitsui Toatsu        Chemicals, KK.                                                                *.sup.2 Aluminum paste, solid content: 65% by Toyo Aluminum Co.               *.sup.3 Benzyltributylammonium chloride                                       *.sup.4 Acid catalyst (effective component: 50%) by KING Industries, Inc.     *.sup.5 ethyl acetate/toluene/Solvesso #150 = 40/30/30 (weight ratio),        dilution of FC #4 = 25 sec.                                              

                  TABLE 8                                                         ______________________________________                                                     Example                                                                       21   22     23     24   25   26                                  ______________________________________                                        Coating                                                                             Base coating M-1    M-2  M-3  M-4  M-5  M-6                                   Clear coating*.sup.1                                                                       1      1    15   13   1    1                               Coating                                                                             Visual appearance                                                                          ∘                                                                        ⊚                                                                   ⊚                                                                   ⊚                                                                   ⊚                                                                   ⊚                perfor-                                                                             Luster       95     98   99   99   98   99                              mance Hardness     F      F    H    H    H    H                                     Acid resistance                                                                            ∘                                                                        ∘-⊚                                                     ⊚                                                                   ∘-⊚                                                     ∘                                                                      ∘-.circleincircl                                                  e.                                    Moisture resistance                                                                        ∘                                                                        ∘                                                                      ⊚                                                                   ⊚                                                                   ∘                                                                      ∘                         Solvent resistance                                                                         ∘                                                                        ∘                                                                      ⊚                                                                   ∘-⊚                                                     ∘                                                                      ∘                         Weatherability                                                                             ∘                                                                        ∘                                                                      ⊚                                                                   ⊚                                                                   ∘                                                                      ∘                         Non-sand recoating                                                                         ∘                                                                        ∘                                                                      ∘                                                                      ∘                                                                      ∘                                                                      ∘                         property                                                                      Temperature  ⊚                                                                     ⊚                                                                   ⊚                                                                   ⊚                                                                   ⊚                                                                   ⊚                      variation crack                                                               resistance                                                                    Scratch resistance                                                                         ∘                                                                        ∘                                                                      ⊚                                                                   ∘-⊚                                                     ∘                                                                      ∘                         Low-temperature                                                                            ∘                                                                        ∘                                                                      ⊚                                                                   ∘-⊚                                                     ∘                                                                      ∘                         curing property                                                         ______________________________________                                         Note                                                                          *.sup.1 Example no. of clear paint used.                                 

                  TABLE 9                                                         ______________________________________                                                  Comparative Example                                                             1      2      3    4    5    6    7                               ______________________________________                                        Acrylic copolymer (A)                                                                     P-12   P-13   P-14 P-15 P-16 P-17 P-18                                        100    100    100  100  100  100  100                             Acrylic copolymer (B)                                                                     G-1    G-1    G-1  G-1  G-1  G-1  G-1                                         80     100    180  60   60   30   130                             Hydroxy group-                                                                containing polymer (E)                                                        Modaflow    0.2    0.2    0.3  0.2  0.2  0.1  0.2                             BTBAC       0.9    1.0    1.4  0.8  0.8  0.7  1.2                             Tinuvin 900 1.8    2.0    2.8  1.6  1.6  1.4  2.4                             Sanol 440   1.8    2.0    2.8  1.6  1.6  1.4  2.4                             Auxi- UVAN 20SE                                                               liary Denacol EX-                                                             curing                                                                              212                                                                     agent                                                                         ______________________________________                                                  Comparative Example                                                             8      9      10   11   12   13   14                              ______________________________________                                        Acrylic copolymer (A)                                                                     p-19   p-20   p-1  p-1  p-1  p-1  p-1                                         100    100    100  100  100  100  100                             Acrylic copolymer (B)                                                                     G-1    G-1    G-10 G-11 G-12 G-1  G-1                                         90     90     360  40   90   90   90                              Hydroxy group-                           H-3  H-1                             containing polymer (E)                   20   80                              Modaflow    0.2    0.2    0.5  0.1  0.2  0.2  0.3                             BTBAC       1.0    1.0    2.3  0.7  1.0  1.1  1.4                             Tinuvin 900 2.0    2.0    4.6  1.4  2.0  2.2  2.8                             Sanol 440   2.0    2.0    4.6  1.4  2.0  2.2  2.8                             Auxi- UVAN 20SE                                                               liary Denacol EX-                                                             curing                                                                              212                                                                     agent                                                                         ______________________________________                                    

                                      TABLE 10                                    __________________________________________________________________________                  Comparative Example                                                           1 2 3 4 5 6 7 8 9 10                                                                              11                                                                              12                                                                              13                                                                              14                                    __________________________________________________________________________    Storage stability                                                                           ⊚                                                                ⊚                                                                X X ∘                                                                   ⊚                                                                Δ                                                                         Δ                                                                         ∘                                                                   ⊚                                                                X ∘                                                                   ∘                                                                   ∘                         Coating                                                                             Visual  ∘                                                                   ∘                                                                   Δ                                                                         Δ                                                                         ∘                                                                   Δ                                                                         Δ                                                                         Δ                                                                         X x x Δ                                                                         Δ                                                                         Δ                               performance                                                                         appearance                                                                    Luster  90                                                                              92                                                                              85                                                                              84                                                                              90                                                                              85                                                                              86                                                                              85                                                                              80                                                                              80                                                                              75                                                                              85                                                                              87                                                                              85                                          Hardness                                                                              HB                                                                              HB                                                                              2H                                                                              2H                                                                              F 2B                                                                              H HB                                                                              H 3B                                                                              2H                                                                              F HB                                                                              B                                           Acid resistance                                                                       Δ                                                                         Δ                                                                         ⊚                                                                ⊚                                                                ∘                                                                   X ∘                                                                   Δ                                                                         ∘                                                                   X ⊚                                                                Δ                                                                         Δ                                                                         X                                           Moisture                                                                              ∘                                                                   ∘                                                                   Δ                                                                         Δ                                                                         ∘                                                                   Δ                                                                         X Δ                                                                         ∘                                                                   Δ                                                                         X ∘                                                                   X Δ                                     resistance                                                                    Solvent Δ                                                                         Δ                                                                         ⊚                                                                ⊚                                                                Δ                                                                         X ∘                                                                   Δ                                                                         ∘                                                                   X ⊚                                                                Δ                                                                         ∘                                                                   Δ                                     resistance                                                                    Weatherability                                                                        Δ                                                                         Δ                                                                         Δ                                                                         Δ                                                                         Δ                                                                         X X Δ                                                                         ∘                                                                   X X Δ                                                                         X Δ                                     Non-sand                                                                              ⊚                                                                ⊚                                                                X X ∘                                                                   X X Δ                                                                         ∘                                                                   X X Δ                                                                         ∘                                                                   ∘                               recoating                                                                     property                                                                      Temperature                                                                           3 3 1 1 3 1 1 2 ⊚                                                                1 1 2 1 3                                           variation crack                                                               resistance                                                                    Scratch Δ                                                                         Δ                                                                         ∘                                                                   ∘                                                                   Δ                                                                         X ⊚                                                                Δ                                                                         ∘                                                                   X ⊚                                                                X ∘                                                                   Δ                                     resistance                                                                    Low-temperature                                                                       Δ                                                                         Δ                                                                         ∘                                                                   ⊚                                                                Δ                                                                         X ∘                                                                   Δ                                                                         ∘                                                                   X ⊚                                                                X Δ                                                                         Δ                                     curing property                                                         __________________________________________________________________________

EXAMPLES 1-20, COMPARATIVE EXAMPLES 1-16

A zinc phosphate-treated steel plate (30 cm×90 cm) was painted with anautomotive cationic electrocoating and baked at 180° C. for 30 minutes.After further coating with an aminoalkyd resin-based second coating andbaking at 160° C. for 30 minutes, the coating was water sanded anddried. After first painting the coating with a base coating (M-1) to adry thickness of 15 μm and letting it stand for 5 minutes, it was thendouble-coated with a clear coating listed in Table 4 or Table 9 to a drythickness of 30 μm, by a wet-on-wet system. After letting the undrieddouble-coated coating stand at room temperature for 15 minutes, it wasbaked for 30 minutes with a hot-air drier at 140° C. (the samples forevaluation of the temperature variation cracking resistance were bakedat 120° C.×25 minutes), to form a multilayer coating by a 2-coat 1-bakesystem. The coating performance of each of the resulting multilayercoatings is shown in Tables 5 and 10.

EXAMPLES 21-26

A zinc phosphate-treated steel plate (30 cm×90 cm) was painted with anelectrocoating and then the coated plate was baked, water sanded anddried, in the same manner as described above. The coating was thencoated with a combination of the base coatings and clear coatings listedin Table 8 by the 2-coat 1-bake method to form a multilayer coating. Thecoating performance of each of the resulting multilayer coatings isshown in Table 8.

The thermosetting coating compositions according to Examples 1-20 of theinvention had excellent storage stability and low-temperature curingproperties, and exhibited superior coating performance.

Furthermore, by forming multilayer coatings with base coatingscontaining the specific thermosetting coating compositions mentioned inExamples 21-26 as essential components and clear coatings which alsoemploy thermosetting coating compositions of the invention, it ispossible to further improve the finished appearance compared tomultilayer coatings which are combinations with known common basecoatings. In contrast, thermosetting coating compositions of ComparativeExamples 1-14 which do not fulfill the conditions specified by theinvention had a lower level of storage stability, low-temperature curingproperties and coating performance.

INDUSTRIAL APPLICABILITY

Thermosetting coating compositions containing acrylic copolymersaccording to the invention have excellent storage stability andlow-temperature curing properties and their use can provide coatingswith excellent coating performance; they are therefore of highindustrial value.

It is claimed:
 1. A thermosetting coating composition comprising anacrylic copolymer (A) containing vinyl monomer units each having anα,β-dicarboxylic acid anhydride group and vinyl monomer units eachhaving an α,β-dicarboxylic monoester group in a total amount of 5-40 wt% and containing the vinyl monomer units with α,β-dicarboxylic acidanhydride groups at 0.3-5 wt %, and an acrylic copolymer (B) with epoxyand hydroxyl groups which has an epoxy equivalent value of 200-1,500g/eq and a hydroxyl group equivalent value of 400-6,000 g/eq.
 2. Athermosetting coating composition according to claim 1, wherein theacrylic copolymer (A) contains 10-70 wt % of (meth)acrylic acid estermonomer units with alicyclic hydrocarbon substituents.
 3. Athermosetting coating composition according to claim 1 or 2, wherein theacrylic copolymer (B) contains 10-60 wt % of (meth)acrylic acid estermonomer units with alicyclic hydrocarbon substituents.
 4. Athermosetting coating composition according to claim 2, wherein the(meth)acrylic acid ester monomer with alicyclic hydrocarbon substituentsis cyclohexyl (meth)acrylate.
 5. A thermosetting coating compositionaccording to claim 1, wherein a methacrylic acid ester monomer unit witha hydrocarbon substituent represented by the following general formula[I] is present in acrylic copolymer (A) in an amount of 5-50 wt % and inacrylic copolymer (B) in an amount of 0-25 wt % ##STR2## wherein R¹represents a hydrocarbon group of 8-18 carbon atoms.
 6. A thermosettingcomposition according to claim 3, wherein the (meth)acrylic acid estermonomer with alicyclic hydrocarbon substituents is cyclohexyl(meth)acrylate.
 7. A thermosetting coating composition according toclaim 1, wherein both acrylic copolymer (A) and acrylic copolymer (B)contain 5-25 wt % of styrene as a monomer unit.
 8. A thermosettingcoating composition according to claim 1, which further comprises ahydroxyl group-containing polymer (E).
 9. A multilayer coating which isformed by the 2-coat 1-bake coating method wherein coating with a basecoating is followed by coating with a clear coating and both aresimultaneously heated to hardness, said base coating comprising athermosetting coating composition whose major component is anamide-crosslinked acrylic copolymer with N-alkoxyalkyl-substituted amidegroups as functional groups, and said clear coating containing athermosetting coating composition according to claim
 1. 10. A multilayercoating according to claim 9, wherein the base coating comprises 2components which are an acrylic copolymer (C) containing at least 2carboxy groups per molecule and an acrylic copolymer (D) containing atleast 2 epoxy groups per molecule, the total resin solid portion of theacrylic copolymer (C) and acrylic copolymer (D) in the base paint being10-50 wt %.
 11. A method of coating a surface, comprising applying thecoating composition of claim 1 to the surface.